The present invention is directed to a cruise control unit for a motor vehicle, which minimizes vehicle operating costs, based on an analysis of vehicle operating parameters and route information regarding a route section ahead of the vehicle.
Conventional cruise control systems seek to maintain vehicle speed at a preset value, which is ordinarily input to the system by an operator of the vehicle. For this purpose, the system includes sensors for detecting actual vehicle speed, which is fed to a controller and compared with the desired vehicle speed. The vehicle throttle is then adjusted based on an error signal and a control algorithm. Such closed loop control systems, which may utilize P, PI, or PID control are well known. In addition, such systems may (but need not) also include sensors for detecting obstacles in the path of the vehicle, and for adjusting the vehicle speed accordingly.
One disadvantage of conventional cruise control systems is that they fail to take into account, environmental parameters regarding the route which is being traveled, such as road gradient and road curvature. Thus, the conventional cruise control system seeks to maintain a vehicle speed at the set value, regardless of whether the vehicle is on an uphill or a downhill grade, or is approaching a sharp curve in the road. However, if a vehicle maintains its speed at a desired value on an uphill grade, then it will pick up speed, possibly exceeding the desired speed on the downhill segment such that the vehicle operator must intervene and apply the vehicle brakes. Similarly, since the cruise control system also maintains vehicle speed when entering a curve, it will frequently be necessary for the vehicle operator once again to intervene by applying the brakes, in order to accommodate the curve. Such wide variations in vehicle speed, as well as the necessity for human intervention in order to apply the vehicle brakes, are wasteful.
Accordingly, it would be advantageous to provide a cruise control system which utilizes information about the current position of the vehicle, as well as stored information concerning upcoming terrain along the route currently being traveled, in order to save fuel and increase driving comfort. In such a system, the current vehicle position may be determined, for example, by means of a Global Positioning System (GPS), and information about the upcoming terrain can be taken from a three-dimensional digital road map for the purpose of controlling vehicle operation.
A system of this generic type is disclosed, for example, in U.S. Pat. No. 6,370,472 B1, in which an optimal set of vehicle control parameters are initially established by having a driver of particularly high skill in the conservation of fuel, drive the vehicle over a predetermined course. As the vehicle proceeds, sensors collect throttle voltage information, as well as time position and elevation data from a GPS receiver. The latter information is stored, together with vehicle speed data in a digital map. Thereafter, when the vehicle once again travels over the same route, an onboard computer uses the previously created optimal driving profile to control the throttle position of the vehicle. For this purpose, the onboard computer uses information read from a GPS sensor to compare the current vehicle position and throttle voltage to the historical data, reads the previously recorded “optimal” data from the digital map, and uses adaptive techniques to match the current throttle voltage to the throttle voltage at the same location based on the historical data established during the optimizing initial run.
For the latter purpose, the '472 system provides for matching the slope of the historical (optimum) run to the current run. That is, the system “looks ahead” a specified distance or time, and determines the slope of the “historical throttle voltage versus time/distance curve”, and applies that slope to the current data to adjust the current throttle position.
One disadvantage to the known prior art systems, such as the '472 patent, is that they require at least one “record drive” to be performed prior to operation of the system. This in turn requires that every route in the road network contained within a potential operating area of the vehicle must first be transited by an expert driver. Furthermore, control of the vehicle throttle based on such historical driver generated information is only as good as the “expert driver” who first traveled the route, establishing the historical profile to control throttle position. To the extent that such driver deviates from the actual optimum operating parameters during the initial “record drive” subsequent vehicles traveling the same route will deviate from the optimum in a corresponding manner.
In addition, unforeseeable driving situations which occurred during driving with automatic throttle control are not considered in the recorded historical throttle profile. Such a situation might arise, for example, where the driver manually overrules the cruise control system (for example, by applying the vehicle brakes) when the vehicle approaches a slower vehicle ahead, or when the cruise control is overruled by another driving system, such as an adaptive cruise control system with distance control. In such situations, it is necessary to adjust the subsequent driving parameters according to a profile which differs from an historical profile in order yet to achieve optimum vehicle operation. However, the prior art systems, such as the '472 patent contain no provision for reconfiguring the system to return to the record/preselected throttle control profile, since the recorded control values are not modified, and do not themselves adapt to changing driving situations in this manner.
Accordingly, one purpose of the present invention is to provide a vehicle control system which continually adjusts vehicle control parameters to optimum values based on current vehicle operating conditions as well as stored route information, using an analytic function to determine an optimal velocity of the vehicle.
Another object of the invention is to provide a vehicle control system which exhibits a high degree of flexibility, and is able to adapt the velocity control to changing driving situations which result from the intervention of external constraints on driving behavior as the vehicle transits a particular route.
Still another object of the invention is to provide such a system which eliminates the need for an initial “record drive” by an expert, as well as the human error introduced into the system as a result of failure by the expert to achieve optimal driving conditions during the record drive.
Yet another object of the invention is to provide a vehicle control system in which optimal vehicle control values are continuously calculated online during operation of the vehicle, taking into account the current vehicle velocity as it transits a particular route.
Finally, another object of the present invention is to provide a vehicle control system which takes into account road curvature information, to adjust the vehicle throttle position.
These and other objects and advantages are achieved by the predictive cruise control system according to the invention, which utilizes information about the current vehicle position, as well as upcoming terrain in order to save fuel and increase driving comfort. The current position is determined by means of a signal received from a Global Positioning System (GPS), and possibly by integration of the vehicle speed over the course of the journey, and information about the upcoming terrain is taken from a three dimensional digital map. The vehicle velocity is then controlled in order to follow an analytically computed optimal driving strategy, based on this information. No previous “record” drive is therefore required.
In the predictive cruise control system according to the invention, a vehicle operating cost function is defined, based on a plurality of environmental parameters, vehicle parameters, vehicle operating parameters and route parameters. As the vehicle travels over a particular route for which route parameters, such as road gradient and curvature, are stored in a road map, sensors aboard the vehicle detect environmental and vehicle operating parameters, including at least vehicle speed and position relative to the road map. As the vehicle proceeds, an onboard computer iteratively calculates and stores in a memory vehicle control parameters that optimize the vehicle operating cost function for a predetermined distance (referred to as a “Prediction Horizon”) along the route ahead of the vehicle. The optimal vehicle control parameters for the Prediction Horizon are then stored in a memory and continuously updated and replaced by new data as the vehicle (and hence the Prediction Horizon) moves along, thereby adjusting the “optimal” control parameters to reflect actual vehicle historical operating experience during the journey. The vehicle is then controlled by reading the optimized vehicle control parameters from the memory, corresponding to the current position of the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.